1. Field of the Invention
The present invention relates to a recording medium suitable for use in ink-jet recording, and also to an image-forming method and a printed article using the medium.
2. Description of the Related Art
An ink-jet recording method is employed to perform recording based on the principle that small droplets of ink are produced to be ejected and entirely or partially attach to a material to be recorded, such as paper, a plastic film coated with an ink-receiving layer, or the like. Recording using the above-mentioned method is performed by the following various ink-ejection processes: ink is electrostatically sucked; mechanical vibration or displacement is provided for ink by use of piezoelectric elements; ink is heated to foam during which a pressure is produced and utilized; and other processes. Attention has been paid to such an ink-jet recording method employed whereby high-speed printing and multi-color printing can be realized, producing very little noise.
Ink used in the ink-jet recording method generally contains water as the main component for reasons of safety and recording characteristics. The ink, in many cases, also contains polyhydric alcohols with a view to preventing clogging of the nozzle and improving ejection stability.
Conventionally, recording media for use in ink-jet recording include: recording paper provided with a coating layer formed on a base paper, which layer contains pulverized silica and a water-soluble binder, such as polyvinyl alcohol or the like, as disclosed in Japanese Patent Publication No. 3-26665; glossy paper provided with a coating formed on cast coated paper, which coating contains polyvinyl alcohol having a degree of saponification of from 50 to 90 mole percent and a crosslinking agent, as disclosed in Japanese Patent Publication No. 3-25352; and over-head projector (OHP) recording sheets provided with a hydrophilic coating formed on a polyester film, which coating contains water-soluble polyvinyl alcohol having a degree of saponification of from 70 to 90 mole percent, as disclosed in Japanese Patent Laid-Open No. 60-220750.
In view of increasing improvements in the performance of ink-jet recording apparatuses, such as higher speed recording and multicolored printing, there is now an increasing need for ink-jet recording media having a better and wider range of characteristics, that is, a need for satisfying all the following characteristics at the same time.
(1) High absorbency with respect to ink (large absorption capacity and high absorption speed with respect to ink); PA0 (2) High optical density of dots and no blurring at their periphery; PA0 (3) Increased roundness of dot shape and smoothness at the periphery of the dots; PA0 (4) Good stability of maintaining the image's quality for a long period without deterioration (in particular, in an environment of high temperature and high humidity); PA0 (5) Inhibiting changes in characteristics in response to changes in temperature and humidity, and preventing curling; PA0 (6) Lack of blocking; and PA0 (7) Good stability of maintaining the quality of the recording medium for a long period without deterioration (in particular, in an environment of high temperature and high humidity).
With respect to OHP recording sheets and the like, there is a further need for excellent transparency of the recording medium.
These characteristics are, in many cases, trade-offs with each other, and it is thus difficult to satisfy all the characteristics at the same time by conventional techniques.
For example, the conventional recording media which have been described above by way of example have reasonably good characteristics, such as dot shape and blocking-resistance properties. However, they are insufficient in absorbency with respect to ink, thus causing ink to overflow in portions having higher image density, i.e., portions to which a larger quantity of ink is directed, which further results in images stained with ink and gives rise to inconsistencies in density. In particular, when color printing is performed, different colored stains occur due to color mixture in the boundaries between different colors.
Recently, there has been a report on the use of black ink and color ink having different surface tensions, in order to inhibit bleeding between black and other colors, as disclosed in Japanese Patent Laid-Open No. 6-136310. However, there are very few recording media exhibiting good recording characteristics for these different types of ink.
In further consideration of other characteristics, such as ink drying time and the like, there is not yet a recording medium which completely satisfies all the characteristics required of an OHP film.
Along with higher speeds of ink-jet recording, higher image densities, improved multi-colored printing, and increasing varieties of ink, come serious problems of long ink drying time, and decreases in image quality and shelf stability of the printed article.
A recording medium provided with an ink-receiving layer formed of polyvinyl pyrrolidone as a main component, as disclosed in Japanese Patent Publication No. 3-29596, has comparatively good ink absorbency in an environment of ordinary temperature and humidity. However, it takes an extremely long time for the ink to dry in an environment of high temperature and high humidity, which further encourages the occurrence of blocking. Also, the recording medium's recording surface has a low mechanical strength and is thus vulnerable to flaws.
The foregoing recording medium provided with an ink-receiving layer formed of polyvinyl alcohol as a main component has comparatively good blocking-resistance characteristics and good mechanical strength of its recording surface. However, after the recording medium has been left for a long time in an environment of high temperature and high humidity, the quality of the medium and its absorbency with respect to ink deteriorate. Also, after an image has been left for a long time in an environment of high temperature and high humidity, dot bleeding occurs, causing a deterioration in image sharpness.
Further, as disclosed in Japanese Patent Laid-Open No. 63-221077, polyvinyl acetal is used as a component of an ink-receiving layer. This can solve the problem of ink absorbency to some extent, but the image sharpness is far from satisfactory, particularly after a recorded image is left for a long time in an environment of high temperature and high humidity.
According to the foregoing recording method in which black ink and color ink having different physical properties, such as surface tension and the like, are used, cation-modified polyvinyl alcohol is used as a component of the ink-receiving layer, as disclosed in Japanese Patent Laid-Open Nos. 61-10483, 60-171143 and 61-235182. Such polyvinyl alcohol is used to obtain considerably satisfactory printing characteristics. However, characteristics other than image, such as ink drying time, tackiness on the surface of the ink-receiving layer and the like, are not sufficiently improved.
Still further, as disclosed in Japanese Patent Laid-Open Nos. 59-95188, 57-93193 and 62-170383, a hydrophilic resin emulsion is used as a component of an ink-receiving layer. However, none of the compositions of the ink-receiving layers specified in the above patent publications can completely solve the above-described problems. Among others, there is still a deterioration in image quality, which is the most important factor, such as ink stains on image and density inconsistencies caused by overflowing ink, particularly in portions having higher image density, that is, portions where a larger amount of ink is used.